1. Field of the Invention
The invention relates to the field of electronic components and informatics and can be used in production external and operative memory, computing and every possible information device.
2. Background Art
In the near future, the main problem of the development of multimedia technology will become processing and accumulating terabit volumes of information. Carriers of information, existing at present, like magnetic, optical and silicon carriers, nearly run out all possibility, both in physical, and in economic plan. Known methods of recording information are based on the principle of modulation of the electron or photon stream, interacting with a medium—a carrier of information.
A prevalent method of information storage is information storage on an electric capacitor or information storage directly in the dielectric of the capacitor on introduced defect—an electron traps [1].
In connection with an advanced stage of development of silicon technology usually for information storage capacitors with dielectrics from SiO2, Si3N4 and so on are used. They have low permittivity ε=4 but high field strength E under which the dielectric breakdown occurs. The field strength will reach E=3*107 V/cm in the thin 15 nm film due to decrease of defects [1, chapter 7.3.4]. In such capacitors, specific density of energy of information storage is of the order W=3.5*102 J/cm3. However, it is really impossible to achieve such energy density because of the oxide film is directly found on the semiconductor.
For instance, in the system Si—SiO2, when the field in silicon reaches the value to be typical of avalanche breakdown 3*105 V/cm, the corresponding field in oxide approximately is three times more (˜106 V/cm) because εSi/εSiO2=11.7/3.9 [1, chapter 7.3.4]. This effect at least reduces density of energy accumulated in the capacitor to one order. High energy density of information storage allows the ratio of the useful signal to noise to increase and, consequently, the record information density to increase to 1 Gbit/cm2. However, high leakage currents are formed because of small film thickness.
For instance, under the field E=6* 106 V/cm the density of the leakage current is ˜4*10−11 A/cm2. Note that leakage currents depend on operating temperature of the instrument exponentially. Besides, the decreasing of the film thickness below 8 nm results in tunnel current appearance in the capacitor. Consequently, these effects limit the time of the charge storage and operating temperature range. So during process of information storage, for instance, in temporary memory, it is necessary to restore the charge periodically—to regenerate. In such mode the dead time necessary on charge regeneration appears, and power consumption of operating memory sharply rises. Besides, such memory loses information when power is off.
To make the energy-independent memory semiconductor FET with enough thickness dielectric layer of control gate are used. The dielectric is made as multi-layer one or defects or additional electrodes are introduced in it. Special control impulse being applied, the dielectric is disrupted and charges are carried in it. They are trapped in the dielectric and can be stored quite long. This charge changes the static properties of the transistor that is used for identification of information in each cell. However, such cells appear to be quite large. This limits the possibility of the making the integrated circuit of large capacity [1,2].
The analog memory with serial access on the base of charge-coupled devices (CCD) is broadly used except in digital integral circuits with random access. They are usually used in photo and television detectors for transformation of the image in digital form. The metal-oxide-semiconductor (MOS) capacitor working in the mode of deep carrier depletion is the main element of a charge-coupled device. This device includes a semiconductor substrate covering by uniform layer of the insulator (the oxide), on which gates—transfer electrodes are located quite close to each other.
Here information as charge packet moves consecutively from cell to cell along the surface under the action of clock pulses applied to transfer electrodes. However, the number of the information shifts is limited by several thousand. In future charge packet degrades. With the clock rate being increased over 107 Hz, the charge packets also degrade. As a result, analog information is lost. If charge-coupled devices are used in the mode of digital information storage, connected information in charge-coupled devices, it is possible to recover periodically the charge as “1” and “0”. Clear the presence of one fault cell in the memory line falls out of the whole line. Therefore, the process of production charge-coupled devices is quite expensive.
Besides, charge in charge-coupled devices is kept in quite a large area—in the depletion located under oxide layer of the semiconductor. This reduces the specific energy of information storage in several orders in contrast with temporary memory with random access, that does not allow the cell size to decrease and the recording density of information above 10 Megabit/cm2 to be achieved. As the result, these devices have not found wide application for making the external memory because of high cost of the unit information storage [1].
To increase the density of recording of information over 1 Gbit/cm2 it is necessary to reduce the size of a storage cells up to sizes, allowing to keep one electron [3,4]. However, experiments have shown that miniaturizing of the cell results in decreasing of the working temperature less than 4K. This is related with that fact that the miniaturizing of the cells of active element simultaneously increases stray permittivity of control electrodes. This accordingly increases the stray noise charge, which destroys useful information keeping in a cell [5].
In this regard, the question, whether it is possible to create the energy-independent memory on capacitor with large specific energy of information storage for obtaining high writing density of information, simultaneously working in wide temperature range and fast response, arises.
The electric capacitors on the base of solid dielectrics, having large specific capacity are known, for instance, capacitors on BaTiO3 dielectric have large permeability ε>1000 and specific capacity on the order of 0.3 F/cm3. Different methods are used for increasing of specific capacity. The most efficient is the nanostructuring of dielectrics of the type BaTiO3 by way of the creation of nanosize clusters with shell [6], or the creation of thin nanosize films with doping by metal [7].
By means of such approach, as the authors confirm, it was managed to increase permittivity up ε=105-106 and to reach specific capacity 100-1000 F/cm3. As the result, it was managed to obtain the specific energy, accumulated in the capacitor on the order of 102−1.3*104 J/cm3. In the capacitor, made on the enumerated above patent, barium titanate is used with a high degree of metal doping. This results in transformation of dielectric to semiconductor. As the result, large leakage currents appear resulting in quick loss of the accumulated energy. Besides, the process of the cracking 100 nm film begins after increasing the energy density over 103 J/cm3. Consequently, the use of such capacitors for long-term keeping of the energy is not effective.
In the solid-state capacitors enumerated above, ion transfer mechanisms are used. So, in BaTiO3, ions are shifted relatively to the crystal lattice. Such process of the heavy ion moving limits the speed properties. So, it is impossible to use such capacitors in memory elements of very-high-speed integrated circuits.